1. Field of the Invention
The present invention relates to an illumination device and a vision measuring instrument. In particular, the invention relates to an illumination device that can change a light irradiation angle toward an object.
2. Description of Related Art
A vision measuring instrument that irradiates illumination light on a to-be-measured object W to measure a shape of the object W based on an image obtained by reflected light from the object W has been known. FIG. 8 shows an overall arrangement of the vision measuring instrument. FIG. 9 shows an inner arrangement of the vision measuring instrument.
The vision measuring instrument 10 includes: a measuring unit 11 that captures an image of the object W mounted on a stage 20; an image processor 21 that analyzes a shape of the object W based on the captured image; and an illumination device 22 that illuminates the object W.
The measuring unit 11 includes: an imaging device 12 that captures an image of the object W; a movement mechanism 15 that three-dimensionally moves the imaging device 12 in accordance with a to-be-measured part of the object W; and the stage 20 on which the object W is mounted. The imaging device 12 includes an objective lens 13 and a CCD camera 14 that captures an image focused by the objective lens 13.
The movement mechanism 15 includes: a portal frame 16 slidable in front and rear directions relative to the stage 20; a Z column 18 in which a beam portion 17 of the portal frame 16 is slidable in right and left directions; and a Z spindle 19 slidable up and down in the Z column 18. The objective lens 13 for imaging the object W is attached on a lower end of the Z spindle 19. The image processor 21 processes image data obtained by the CCD camera 14.
Note that, in FIG. 9, an optical axis A of the objective lens 13 is defined as the central axis of the vision measuring instrument 10.
The illumination device 22 is attached on the lower end of the Z spindle 19 with the objective lens 13 inserted at the center of the illumination device 22. Light beams circularly arranged around the central axis (the optical axis A) are irradiated toward the object W to evenly illuminate the object W.
The illumination device 22 includes: a ring casing 23 of which lower side is open and upper surface has an insertion hole at its center; and an illuminating optical system 24 that is disposed inside the casing 23 and circularly irradiates light beams from the lower side of the casing 23.
The illuminating optical system 24 includes a plurality of LEDs 25 (light sources for light emission) circularly distributed in the overall interior of the casing 23; a reflecting mirror 26 that reflects light from the LEDs toward the object W; and dichroic mirrors 27 that introduce the light from the LEDs to the reflecting mirror 26.
The LEDs 25 emit light downward. The dichroic mirrors 27 are disposed on a lower side of the LEDs 25 and have concave surfaces to reflect the light from the LEDs 25 substantially horizontally toward the opposite side of the central axis (the optical axis A). The reflecting mirror 26 is disposed on the opposite side of the central axis (the optical axis A) relative to the dichroic mirrors 27 and has a concave surface to reflect the light from the dichroic mirrors 27 obliquely downward toward the central axis.
In the arrangement, to capture an image of the object W, initially the object W is mounted on the stage 20. Then, the illumination device 22 circularly irradiates light beams to illuminate the object W. More specifically, the light irradiated from the LEDs 25 is reflected by the dichroic mirrors 27 toward the opposite side of the central axis (the optical axis A), which is then reflected by the reflecting mirror 26 obliquely downward toward the central axis to be incident on the object W. The light reflected by the object W is captured by the CCD camera 14 via the objective lens 13. Image data from the CCD camera 14 is image-processed by the image processor 21, with which inspections are conducted, for instance, to detect an edge of the object W or dust or a scratch on the object W or to measure the size thereof.
By changing the light irradiation angle toward the object W, a surface shape such as the edge can be emphasized. In order to change the light irradiation angle toward the object, the position of the reflecting mirror 26 needs to be changed. As shown in FIG. 10, when the dichroic mirrors 27 and the reflecting mirror 26 are moved at the same speed, the light incident position on the reflecting mirror 26 will not be changed. Accordingly, it is impossible to change the light irradiation angle toward the object W.
To solve the problem, as shown in FIG. 11, it is suggested that the dichroic mirrors 27 and the reflecting mirror 26 be moved at different speeds (the dichroic mirrors 27 are moved faster than the reflecting mirror 26) to change the relative positions of the dichroic mirrors 27 and the reflecting mirror 26 in accordance with the movements (see JP-A-62-168125).
With the arrangement, the light incident position on the reflecting mirror 26 is changed as the position of the reflecting mirror 26 relative to the dichroic mirrors 27 changes, so that the light irradiation angle toward the object W can be changed. Further, by changing the light irradiation angle toward the object W, the surface shape of the object can be emphasized, so that the position of the edge or the size of the object W can be highly accurately detected based on the image data.
However, a mechanism in which gears are complexly combined is required to move the dichroic mirrors 27 and the reflecting mirror 26 at different speeds as suggested above. Accordingly, the illumination device 22 becomes extremely large and costs for preparing and assembling components thereof will be extremely increased.